In September 2025, the U.S. Environmental Protection Agency (EPA) issued a new enforcement alert focused on benzene fenceline monitoring at petroleum refineries. Facilities that exceed benzene action levels are required to conduct a root cause analysis (RCA) and implement corrective actions promptly. Noncompliance could result in civil penalties, additional control requirements, or consent decree obligations.

This alert follows EPA’s continued focus on fenceline monitoring under the Refinery Maximum Achievable Control Technology (MACT) program, which is part of 40 CFR 63 Subpart CC. The agency stresses that exceedances must be investigated thoroughly, even if emissions originate from fully compliant sources or offsite areas adjacent to the refinery, to prevent community exposure to benzene.

Fenceline Monitoring Requirements

Under the fenceline program, facilities are required to collect samples from passive tube monitors every 14 days. After each sampling period, the facility calculates the theoretical benzene impact (Δc) and tracks the rolling annual average using the 26 most recent 14-day periods. If the annual average exceeds the action level, the facility must:

• Initiate a RCA within 5 days of determining the exceedance.

• Complete initial corrective actions within 45 days to reduce benzene concentrations.

Facilities must document all exceedances, investigations, and corrective actions. EPA notes that compliance involves more than just meeting monitoring requirements; facilities must proactively identify and address the source of elevated benzene levels, regardless of whether the source is considered compliant under other regulations.

Challenges in Identifying Sources

Two-week sampling intervals can make pinpointing emission sources difficult, particularly if the source has stopped emitting by the time the investigation begins. EPA recommends several investigative tools and strategies to address this challenge:

• Real-time gas chromatographs: Allow near-instantaneous benzene concentration measurements, which can be correlated with wind direction to identify potential emission sources.

• FLIR cameras: Forward-looking infrared cameras can quickly scan large areas for leaks, identifying sources that passive sampling may miss.

• Benzene-specific handheld detectors: Portable photoionization detectors allow pinpointing benzene emissions at specific points or interfaces.

• Data integration: Combining fenceline monitoring data with operational logs, meteorological information, and process records can help narrow down potential sources and validate findings.

By using these tools in combination, facilities can detect sources more accurately, reduce the risk of repeat exceedances, and provide defensible documentation in case of regulatory review.

Frequent Sources of Exceedances

EPA has noted several common areas where benzene action level exceedances frequently occur:

• Storage tanks: Tanks containing high-benzene liquids such as reformate, light naphtha, or pyrolysis gasoline from co-located ethylene plants.

• Marine loading operations: Non-tight loading arms, improper slop disposal from loading arm drips, and barge pressure relief valves lifting during loading or while docked.

• Wastewater operations: Dissolved air flotation systems, aerated biological treatment units, and uncontrolled junction boxes.

By identifying high-risk areas, refineries can implement preventive measures such as additional monitoring, equipment upgrades, and more frequent inspections to avoid exceedances before they trigger enforcement action.

Regulatory Context

Benzene fenceline exceedances often intersect with the Benzene Waste Operations NESHAP (BWON) program. Recent EPA enforcement cases, including the 2025 HF Sinclair Navajo Refining LLC consent decree, the 2024 Lima Refining Company consent decree, and the 2023 BP Products North America Inc. consent decree, illustrate that even when underlying units comply with permit requirements, EPA may require additional controls, expanded monitoring, or enhanced investigative measures.

Consent decrees from these cases have included requirements such as installation of additional monitoring points, real-time detection systems, corrective action plans, and routine reporting of benzene concentrations. Facilities that fail to respond promptly risk penalties, increased regulatory oversight, or costly mandated upgrades.

Practical Steps for Refineries

Refineries can take several proactive steps to minimize risk and ensure compliance:

• Update fenceline monitoring programs to ensure all sampling points, schedules, and calculation methodologies are current and meet EPA expectations.

• Prepare for rapid response by establishing internal procedures for initiating RCA’s within the required 5-day window and implementing corrective actions within 45 days.

• Implement additional investigative tools such as real-time monitoring, FLIR cameras, and benzene-specific handheld detectors to provide faster source identification and more detailed data for corrective action planning.

• Maintain thorough documentation of exceedances, investigations, corrective actions, and supporting data to demonstrate due diligence during inspections.

• Cross-functional collaboration between operations, environmental, and maintenance teams to identify potential sources, evaluate risk, and implement solutions before enforcement actions occur.

• Community communication for refineries adjacent to residential areas to improve transparency and reduce public concern.

How Trinity Can Help

Trinity can provide specialized support for refineries navigating EPA fenceline enforcement, including:

• Real-time fenceline monitoring using Open Path Technologies.

• Facilitation of RCA’s and development of corrective action plans.

• BWON/QQQ program audits and site-specific monitoring plan preparation.

• Strategic guidance for aligning internal compliance programs with EPA expectations.

• Training and support for operations and environmental teams to enhance investigative and reporting capabilities.

Refineries can leverage Trinity’s expertise to reduce the likelihood of exceedances, respond effectively to EPA enforcement alerts, and demonstrate a proactive commitment to environmental compliance and community safety.

If your refinery is preparing for fenceline monitoring, responding to a benzene exceedance, or needs support with RCA and corrective action planning, our team is ready to help. Trinity’s experts can assist with monitoring strategies, investigative tools, and compliance documentation to ensure your site meets EPA requirements efficiently. Contact us at 734.474.7709 to discuss your fenceline program or to schedule a review of your facility’s benzene monitoring and response procedures.